A simple random sample (SRS) is a subset of a population in which every member has an equal chance of being selected, and every possible subset of the desired size has the same probability of being chosen. This makes the sample representative of the population with minimal selection bias, assuming the sampling frame is complete and data collection is unbiased. If you’d like, here’s a quick guide to implementing a simple random sample in practice:
- Define the population and sampling frame: Identify the group you want to study and ensure you have a complete list of its members.
- Determine the sample size: Decide how many individuals to include based on your research questions, desired precision, and available resources.
- Assign unique identifiers: Label each member of the sampling frame with a unique number from 1 to N (where N is the population size).
- Draw random numbers: Use a random number generator or randomization function to select the required number of unique identifiers corresponding to your sample size.
- Collect data: Reach out to the selected individuals and collect your data, ensuring consistency in measurement and minimizing nonresponse bias.
- Check for biases: Assess the sampling frame for coverage gaps (people who are missing from the frame) and consider potential nonresponse bias.
Key contrasts to keep in mind:
- SRS vs systematic sampling: SRS is purely random; systematic uses a fixed interval (e.g., every 10th person) which can be more practical but may introduce bias if there’s hidden order.
- SRS vs stratified sampling: SRS treats the entire population as one group; stratified sampling divides the population into subgroups (strata) and samples within each, which can improve precision when strata are homogeneous.
- SRS vs cluster sampling: SRS samples individuals directly; cluster sampling samples groups (clusters) and then may sample individuals within selected clusters, often used when a complete list is hard to obtain.
If you share details about your population, frame, and desired sample size, a tailored step-by-step plan can be provided.
